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Feb. 16, 2011 -- When it comes to taking medicine, you may get what you expect.

A new study has found that your expectations can affect how well pain medications work. Being optimistic may boost their effectiveness in blocking pain, while being pessimistic may lower their effectiveness.

Unlike earlier research, the new study used brain imaging techniques to examine brain regions that are known to be associated with pain.

Scientists say that until now, little research has been done to clarify the brain mechanisms that control how different expectations affect drugs.

The study is published in the Feb. 16 issue of Science Translational Medicine.

The Power of Expectations

German and British researchers used brain scans to study how positive or negative expectations affected brain activity in a group of healthy people.

The researchers used a heat source to cause pain to the volunteers and scanned their brains while administering pain medication.

The researchers write that expectations that the pain medication would be effective doubled the effect of the drug, while a negative or gloomy outlook made the pain reliever less effective. The pain medication used was Ultiva, an IV drug generally used during surgery.

“Doctors shouldn’t underestimate the significant influence that patients’ negative expectations can have on outcome,” Irene Tracey, of Oxford University’s Center for Functional Magnetic Resonance Imaging of the Brain, says in a news release.

Twenty-two healthy volunteers took part in the study. They were given the pain medicine and placed in an MRI scanner. Heat was applied to a leg at a level sufficient for each person to rate the pain at 70 on a scale of 1 to 100. An intravenous line was used to administer the pain medication.

Unknown to the volunteers, the researchers started giving the drug to see what effects it would have in the absence of any knowledge or expectation of treatment. The average initial pain rating of 66 went down to 55.

Then the participants were told the drug would start being administered, though no change was made in the medication dose. Still, the average pain ratings dropped further, to 39.

Lastly, the volunteers were made to think the pain relief medicine had been stopped (when it was actually continued) and were warned pain might increase. And it did, at least according to the volunteers’ perception, who then rated pain at 64, even though they were receiving the same amount of the drug.

The MRI scans showed that the brain’s pain networks responded according to the expectations of the volunteers.

Tracey says clinicians need to be aware of the power of expectations on any type of treatment.

Studying Brain Activity

Study researcher Ulrike Bingel found that expectation of increased pain was accompanied by increased activity in a number of brain regions, including the hippocampus, the mid-cingulate cortex, and medial prefrontal cortex. Those areas are known to mediate mood and anxiety.

In addition, when there was expectation of pain reduction, the researchers noticed increased activity in the anterior cingulate cortex -- thought to be involved in rational cognitive functions and reward anticipation -- and the striatum, which plays a role in movement and balance.

Authors of an article published with the study write that the Bingel study indicates a “large inter-individual variability in response to placebo treatment” and that it’s time to incorporate knowledge about placebo effectiveness in daily medical practice.

Bingel tells WebMD in an email that the study opens a new avenue of research on the connection between drugs, personality, therapeutic context, and disease.